The present invention concerns a bistable piezoelectric generator. More specifically, the invention concerns an electric power generator based on the conversion of mechanical energy into electric energy through the bistable oscillations of elements of piezoelectric material.
It is well known that piezoelectric generators are commonly used in a number of fields of human activity in order to provide electric currents by means of mechanical energy conversion. However, the limited quantity of electric energy produced by conventional generators tends to limit their use. In recent years a number of studies have been proposed wherein the power generated by piezoelectric material could be employed to power mini and micro portable electronic devices. Such devices require just a limited amount of electric power during their operation, allowing the use of power micro-generators as an alternative to traditional batteries. In this respect, there have been proposed power micro-generators that can be connected to devices or structures undergoing some kind of movement (table vibrations, benches or mechanical structures vibrations, oscillatory motions made by machines or cars, human or animal motion, natural atmospheric or seismic event activated motion). Such devices convert the energy present in the environment into electric energy that can be used to power electronic micro devices.
In the past, a number of devices aimed at the same purposes of the present invention have been proposed. Examples can be found in the following U.S. patents.: U.S. Pat. No. 2,081,862 by Alfred L. W. Williams; U.S. Pat. No. 4,467,236 by Henry H. Kolm and Eric A. Kolm; U.S. Pat. No. 4,510,484 by D. S. Snyder; U.S. Pat. No. 4,504,761 by C G. Triplett; 5,512,795 by Michael Y. Epstein et al; U.S. Pat. No. 6,407,484 by John R. Oliver et al; U.S. Pat. No. 6,438,193 by W. H. Ko e; U.S. Pat. No. 7057330 by Steven A. Buhler et al.
The main limitation of the existing devices, however, is their intrinsic inability to exploit the whole spectrum of energy available. This is due to the fact that their functioning principle unavoidably selects just a small portion of the whole energy spectrum. The kinetic energy freely available in the environment (natural events, machine, animal or human related motion) is usually spread in a wide spectrum of frequencies ranging from a few Hz to a few KHz. The existing generators are based on linear oscillations of mechanical piezoelectric structures. Such structures are capable of exploiting the environment's energy only in a narrow frequency band close to their resonant frequency because, for geometrical reasons, they oscillate mainly at their resonant frequency.
On the other hand, a bistable oscillator is a nonlinear oscillating system that, unlike a linear system, admits two equilibrium positions (see graph in FIG. 1). For the linear oscillator, the oscillations are represented by periodic movements centered around the single equilibrium point. For the nonlinear bistable oscillator, the oscillations are represented by a more complex motion. In addition to the two simple oscillations centered around each local equilibrium point, there are also wide movements that represents the passage from one equilibrium point to the other.
Based on these premises, the Applicant has realized a Bistable piezoelectric generator that is capable of overcoming the above mentioned limitations of linear piezoelectric generators.